1. Field of the Invention
The present invention relates to a toner for developing an electrostatic image. In addition, the present invention also relates to a developer including the toner, and an image forming method and an image forming apparatus using the toner.
2. Discussion of the Background
Recently, a need exists for a low end laser beam printer which is low-cost and compact and which can perform high speed printing. In order to miniaturize a laser beam printer, a technique in that an intermediate transfer medium is supported by two rollers instead of three rollers is proposed. In this case, discharging tends to occur in a gap between the intermediate transfer medium and a sheet of an image receiving material to which a toner image is to be transferred from the intermediate transfer medium. In addition, it is necessary to shorten the passage through which an image receiving material sheet is fed so that a toner image is transferred and fixed thereon. When a double sided copy is produced in such an image forming apparatus, the time period of from heat fixation of an image on a first side of an image receiving material sheet to transfer of another image on a second side of the receiving material is very short. In this case, the electric resistivity of the receiving material sheet increases in the heat fixation process, and thereby a problem in that the second image cannot be well transferred onto the second side is caused.
Further, in order to miniaturize an image forming apparatus while reducing the costs thereof, it is necessary for the image forming apparatus to use a two-roller fixing device without an oil applicator. The toner used for such an image forming apparatus needs to include a release agent. However, the adhesiveness of the toner to image forming members such as photoreceptors and intermediate transfer media increases, thereby causing problems such that a toner image cannot be well transferred (i.e., defective image transfer) and/or a transferred toner image has an omission therein.
In attempting to solve the defective image transfer problem caused by change of the electric resistance of an image receiving material sheet, published unexamined Japanese patent application No. (hereinafter referred to as JP-A) 2004-069941 discloses a technique in that after being previously heated, an image receiving material sheet receives toner images on both sides thereof while being subjected to one-pass feeding. The purpose of this technique is to prevent occurrence of the defective image transfer problem caused by change of moisture in a receiving material sheet.
In addition, in attempting to solve the defective image transfer problem caused by change of the thickness of image receiving material sheets, JP-A 2005-189520 discloses an image forming method including the steps of obtaining information on the properties of the receiving material; and controlling the image transfer conditions on the basis of the properties of the receiving material.
Because of these reasons, a need exists for a toner (or an image forming method and apparatus), which can produce high quality images on both sides of image receiving materials.